Semiconductor light-emitting devices such as light-emitting diodes (LEDs) and laser emitting devices such as laser diodes are used in an increasing number of applications. LEDs, for instance, are widely used in general illumination applications while laser diodes are commonly used in long-distance communication applications, optical applications and various imaging applications. As the use of these devices has increased, so too have various application demands for more precise operation of the devices. LEDs need to meet particular brightness, stable light point and ratio of light output requirements, and laser diodes need to meet particular lasing wavelength requirements, both while maintaining adequate operational lives.
Among the operational requirements of both LEDs and laser diodes is a minimum degree of temperature control. In LEDs, light output varies with the junction temperature of the LED, affecting intensity and causing spectral shift. In laser diodes, the emission wavelength varies with the junction temperature of the laser diode. Generally, the power delivered to the LED or laser diode package is controlled by a feedback loop that includes an estimation of the temperature of the package. One or more thermal sensors are often attached to the package to estimate the operating temperature. A thermistor or thermocouple may be used, for example. Among the deficiencies of such a thermal sensor is its lack of proximity to the semiconductor die in which the diode is formed, which can result in errors when estimating junction temperature. This lack of precision may not be acceptable in many of today's applications for LEDs and laser diodes.